Optimizing light path uniformity in inspection systems

Abstract

An inspection system includes an illumination source configured to illuminate a blazed phase grating sample, image collection pathways and an imaging system configured to capture an image of a sample point of the blazed phase grating sample, and a controller configured to adjust the illumination source in response to an analysis of the image of the sample point to determine illumination uniformity of the inspection system.

1. An inspection system comprising:
 an illumination source configured to illuminate a blazed phase grating sample comprising relief gratings at a plurality of angles and relief depths, each relief grating angle adapted to direct light through a different azimuth of a pupil of the inspection system; 
 image collection pathways and an imaging system configured to capture an image of a sample point of the blazed phase grating sample; and 
 a controller configured to adjust the illumination source in response to an analysis of the image of the sample point to determine illumination uniformity of the inspection system, the analysis being based on a comparison of maximum image intensities for each azimuth. 
 
   
   
     2. The inspection system of  claim 1 , further comprising:
 a beam steering component configured to steer light from the illumination source to the blazed phase grating sample, 
 wherein the controller is configured to adjust the beam steering component in response to the analysis of the image of the sample point. 
 
   
   
     3. The inspection system of  claim 1 , wherein the controller is configured to adjust the imaging system m response to the analysis of the image of the sample point. 
   
   
     4. The inspection system of  claim 1 , wherein the controller is configured to adjust the image collection pathways in response to the analysis of the image of the sample point. 
   
   
     5. The inspection system of  claim 1 , wherein the illumination source is configured to illuminate the blazed phase grating sample in a darkfield inspection mode. 
   
   
     6. The inspection system of  claim 1 , wherein the controller is configured to perform the analysis of the image of the sample point. 
   
   
     7. An inspection system comprising:
 means for providing a blazed phase grating sample configured to reflect light through a plurality of azimuths of a pupil of an inspection system; 
 means for obtaining an image of a sample point of the blazed phase grating sample in the inspection system; 
 means for analyzing the image to determine illumination uniformity of the inspection system; and 
 means for adjusting the inspection system based on the analysis to optimize the illumination uniformity of the inspection system; 
 wherein the means for analyzing the image comprises:
 means for determining a maximum image intensity for each azimuth; 
 means for comparing the maximum image intensities; and 
 means for generating feedback based on the comparison for adjusting the inspection system. 
 
 
   
   
     8. A method for optimizing the illumination uniformity of an inspection system, the method comprising:
 providing a blazed phase grating sample configured to reflect light through a plurality of azimuths of a pupil of an inspection system; 
 obtaining an image of a sample point of the blazed phase grating sample in the inspection system; 
 analyzing the image to determine illumination uniformity of the inspection system; and 
 adjusting the inspection system based on the analysis to optimize the illumination uniformity of the inspection system; 
 wherein analyzing the image comprises:
 determining a maximum image intensity for each azimuth; 
 comparing the maximum image intensities; and 
 generating feedback based on the comparison for adjusting the inspection system. 
 
 
   
   
     9. The method of  claim 8 , further comprising:
 comparing the illumination uniformity of the inspection system to a previously obtained illumination uniformity of the inspection system to determine an effect of adjusting the inspection system based on the analysis. 
 
   
   
     10. The method of  claim 8 , wherein providing the blazed phase grating sample comprises exposing a blazed phase grating reticle including at least one array of blazed phase gratings in an exposure tool. 
   
   
     11. The method of  claim 8 , wherein adjusting the inspection system comprises adjusting an illumination source of the inspection system. 
   
   
     12. The method of  claim 8 , wherein adjusting the inspection system comprises adjusting an illumination beam steering component of the inspection system. 
   
   
     13. The method of  claim 8 , wherein adjusting the inspection system comprises adjusting an image capture element of the inspection system. 
   
   
     14. A method for optimizing the light path uniformity of an inspection system, the method comprising:
 providing a blazed phase grating sample comprising relief gratings at a plurality of angles and relief depths, each relief grating angle adapted to direct light though a different azimuth of a pupil of the inspection system; 
 obtaining an image of the sample in an inspection system; 
 analyzing the image to determine a maximum image intensity for each azimuth; 
 comparing the maximum image intensities for each azimuth; 
 providing feedback to the inspection tool based on the comparison; and 
 adjusting an illumination element of the inspection system based on the feedback. 
 
   
   
     15. The method of  claim 14 , wherein adjusting an illumination element comprises adjusting one of an illumination source and an illumination beam steering component. 
   
   
     16. The method of  claim 14 , further comprising:
 adjusting an image capture element of the inspection tool based on the feedback. 
 
   
   
     17. The method of  claim 16 , wherein adjusting an image capture element comprises adjusting one of an objective and an imaging system.